MRS and Optical Imaging Studies of Therapeutic Response to Combination Therapy Targeting BRAF/MEK in Murine Melanomas.

Rationale And Objectives: Melanoma, an aggressive skin cancer, often harbors BRAFV600E mutations driving tumor progression via the mitogen-activated protein kinase (MAPK) pathway. While targeted therapies like BRAF (dabrafenib) and MEK (trametinib) inhibitors have improved outcomes, resistance linked to metabolic reprogramming remains a challenge. This study investigates metabolic changes induced by dual BRAF/MEK inhibition in a BRAFV600E-mutant murine melanoma model using magnetic resonance spectroscopy (MRS), optical redox imaging (ORI), and biochemical assays. We aim to identify metabolic biomarkers for predicting therapeutic response or resistance.

Materials And Methods: YUMM1.7 murine melanoma cells and tumored mice were treated with dabrafenib and trametinib. ORI assessed mitochondrial redox status by measuring reduced nicotinamide adenine dinucleotide (NADH), oxidized flavoproteins (Fp), and the redox ratio (Fp/(NADH+Fp)) in vitro. Glucose consumption and lactate production were analyzed using a YSI Biochemical Analyzer. In vivo metabolic changes were monitored via ¹H and ³¹P MRS, evaluating lactate, alanine, pH, βNTP/Pi, and total NAD(P)(H), which represents combined oxidized nicotinamide adenine dinucleotide (NAD), NADH, and reduced nicotinamide adenine dinucleotide phosphate (NADPH).

Results: Under the combined therapeutic regimen of dabrafenib and trametinib, YUMM1.7 murine melanoma cells exhibited significant inhibition of lactate generation, non-significant reduction of glucose utilization, decreased intracellular levels of NADH and total NAD(P)(H), and more oxidized redox status in vitro, which can be interpreted as inhibition of the Warburg effect and improved OXPHOS efficiency by targeting BRAF/MEK signaling activities. Furthermore, YUMM1.7 mouse tumors demonstrated less tissue acidification and improved bioenergetics (βNTP/Pi), in agreement with the in vitro data.

Conclusion: MRS, ORI, and biochemical assays identified critical metabolic changes, highlighting potential biomarkers and supporting the integration of metabolic inhibitors with MAPK-targeted therapies to improve clinical outcomes.